The present invention relates generally to monitoring a battery's state-of-health.
A vehicle's electrical power supply system must support a plurality of vehicle functions that operate on electrical energy. Such functions include normal vehicle operation devices and safety related devices such as rear window defogger, anti-lock braking/stability systems, lighting systems, etc. In addition to these devices, the vehicle's electrical power supply system also supports comfort, convenience, and entertainment devices. Some examples include air conditioning, heated seats, video/audio systems, and accessory outlet convenience devices. Moreover, with the advent of new X-by-wire technologies (e.g., steer-by-wire, brake-by-wire, etc.), even more electrical power must be demanded of the vehicle's electrical power system. As a result, the increasing electrical power demands from various vehicle electrical devices shorten the useful life of vehicle batteries.
The drain on the battery is related to not only the number of electrical devices used, but also the electrical draw and usage of such electrical devices. Therefore, on-board battery state monitoring systems attempt to determine when a battery may fail. On-board vehicle state-of-health (SOH) information is typically derived from model parameters of an equivalent circuit battery model, which requires the use of a costly current sensor needed to measure high current during cranking. These methods use constant thresholds on selected battery model parameters to determine battery end-of-life, but the calibration of such constant thresholds is complicated due to the variations of battery types, vehicle starting systems, and operating environment.